The present disclosure relates to joined pipe flanges and, more particularly, a fluid control device secured between pipe flanges. Even more particularly, the present disclosure relates to a fluid control assembly adapted to be secured between two pipe flanges and including flange spacers.
Pipes and fluid control devices, such as valves and pumps, are common in the utility, refinery, manufacturing, chemical and petrochemical industries for transporting fluids. Pipes often include attachment flanges at their ends, and fluid control devices are secured between the pipe flanges, usually using bolts. In such cases it is desirable that stresses be applied to the pipe flanges evenly, that the fluid control device is properly aligned with the pipes, and that the bolts are correctly torqued or loaded.
For example, fiberglass reinforced pipe (xe2x80x9cFRPxe2x80x9d) as well as other plastic piping systems and components provide many industries with a corrosion-resistant, less costly replacement for metal piping. However, since plastic piping is, by its nature, not as strong as metal piping, flanges of plastic piping may be more susceptible to cracking upon uneven loading or rotation of the flanges.
Improper alignment of the fluid control device with the pipes could interfere with operation of the fluid control device. Butterfly valves, for example, typically include a generally cylindrical body which is connected into a pipe line by being clamped between two pipe flanges. The valve body has a flow-way therethrough and a valve element is mounted in the flow-way for movement from a closed valve position to an open valve position. In the open valve position, the valve element can extend out of, and beyond the valve body. Thus, correctly aligning the valve with the pipes is necessary to prevent interference between the valve element and the pipe flanges during movement of the valve element between the closed and open positions.
In addition, bolt creep and improper loading or torquing of bolts joining the pipe flanges to the fluid control device can result in a loosening or weakening of the joint. Bolt creep is a condition wherein bolts naturally loosen over time due to machine vibration and thermal expansions and contractions, for example. Improper loading can occur due to inaccurate torquing of bolts holding flanges together.
In many industries it is important not only to prevent leakage of materials from pipes at the pipe-flange/fluid-control device interface under normal operating conditions, but also to reduce the possibility of leakage of materials after exposure to abnormal conditions, such as high heat or flames. In some industrial applications leakage of materials may eventuate hazardous conditions or catastrophic failures. It is therefore a real concern that seals be maintained during such abnormal conditions so that plant personnel can shut down the system in which such seals are employed.
Thus, what is desired is a fluid control assembly for clamping between pipe flanges that provides reduced flange stresses, provides effective sealing under abnormal conditions such as fire, and easy alignment with the pipes. What is also desired is a fluid control assembly wherein bolt creep is reduced or eliminated, and wherein bolt loading is made easy and convenient, both in the assembly of the joint and in the maintenance of the joint.
Accordingly, the present disclosure provides a fluid control assembly including a fluid control device and a relatively non-compressible flange spacer. The fluid control device has a main body, an annular shoulder extending from the main body, and a tubular, relatively compressible liner extending out of the body through and axially beyond the shoulder. The relatively non-compressible flange spacer is positioned on the shoulder and extends from the main body to between an end of the shoulder and an end of the liner, when the liner is in a non-compressed state. Whereby, the flange spacer prevents a pipe flange secured to the fluid control device from bending, or xe2x80x9crotatingxe2x80x9d, when clamped to the device, thereby substantially eliminating uneven stresses on the pipe flange. The flange spacer also allows the liner to be compressed, but not over-compressed and damaged, such that the compressed liner provides a fluid-tight seal between the fluid control device and the pipe flange, yet does not interfere with movement of a valve member within the liner.
According to one preferred embodiment, the flange spacer is a composite assembly comprising compressible fire-resistant material (that is, resistant to deformation when subjected to a flame and the heat associated with typical industrial fires), such as flexible graphite, bonded to a relatively non-compressible material, such as a solid metal. The compressible fire-resistant material is preferably bonded along the major surfaces of the flange spacer that are intended for contact with the flanges of the pipe and the fluid control assembly. For example, flexible graphite may be bonded to each major face of a carbon steel ring to form a three-ply laminate assembly that acts as the flange spacer. Preferably, the compressible fire-resistant material is a low-density material which increases its density as its thickness decreases. The increase in density creates a homogenous gasket and eliminates permeating fluid from escaping through its wall. That is, the compressible fire-resistant material preferably acts as a gasket. In a preferred application, a composite flange-spacer is placed about each shoulder of the fluid control assembly and is articulated between the valve body and the pipe flange. When flexible graphite is employed, it is preferred that the graphite faces are compressed from a nominal thickness to approximately half its nominal thickness after final compression. Preferably, a mating pipe liner is simultaneously compressed against the mating valve liner in order to create a face seal for the process fluid. In the event of a fire, while the mating valve liner and pipe liner may soften, burn or disintegrate (depending on the exposure time), the composite flange spacer will remain and the flexible fire-resistant material will retain its seal with the valve body and mating pipe-flanges (by impinging on the same). This prevents process fluid from escaping into the environment. Thus, while the plastic materials may burn or disintegrate, the seal is maintained, at least to an extent that plant personnel can have time to shut down any process employing such fluid control assembly, or to drain the pipes connected with such fluid control assembly.
As would be understood by one of ordinary skill in the art, the invention described may employ any valve type, in particular, any flanged style valve such as, but not limited to, a gate, globe, ball, plug and butterfly. Further, as would be understood by such person, the composite flange spacer would have particular use in applications where the risk of fire or extended temperatures might be feared to destroy the pipe and flange linings since these are often fabricated from rubber or plastic material.
According to one aspect, the flange spacer comprises a perimeter spacer ring having an inner diameter equal to an outer diameter of the annular shoulder. According to another aspect, the fluid control assembly is for connection to a pipe flange and the perimeter spacer ring has an outer diameter equal to an outer diameter of the pipe flange, such that the ring allows the fluid control device to be easily and properly aligned with the pipe flange.
According to an additional aspect, the main body of the fluid control device includes bolt holes passing therethrough and the perimeter spacer ring has bolt openings corresponding to the bolt holes of the fluid control device. According to a further aspect, the fluid control assembly further includes bolts for securing the fluid control assembly to a pipe flange, and a liveload assembly positioned on each bolt for preventing bolt creep and maintaining clamping pressure on the flanges. Each liveload assembly includes an upper washer, a lower washer, and at least one spring positioned to resist compression between the upper and the lower washers.
According to still another aspect, the liveload assemblies also include a ribbon secured at a first end to one of the upper and the lower washers, with a second end of the ribbon extending towards the other of the upper and the lower washers. The ribbon has a total length, including a comparison portion substantially equal to a proper compressed height of the at least one spring, with only the comparison portion of the total length positioned between the upper and the lower washers for comparison with the height of the spring.